Qualitative analysis for residues of biphenyl, orthophenylphenol and sodium orthophenylphenate in citrus fruit peel. ... Apparatus. mixer250 ml flask with ground glass joint and with a cooled reflux condenser reduced pressure evaporator micropipettes thin layer chromatographic apparatus with plates measuring 20 X 20 cmU.V. lamp (254 nm): the intensity should be such that a spot of 5 µg of biphenyl is visible equipment for pulverising reagents oven ...